Computer networks facilitate communication between computers, and between computers and stand-alone peripherals. Computer networks enable large scale computing systems, distributed service systems, and a whole host of applications that would otherwise be infeasible. Thus, incentives exist for the use and enhancement of computer network technology. As computer networks increase in speed and size, they require more sophisticated protocols to ensure fast and reliable communications.
Storage area networks (SANs) are a popular type of computer network. SANs are networks of data storage devices (e.g. RAID units). The SAN is usually a sub-network of a larger computer network that includes servers and personal computers. SANs provide a large, shared storage capacity that has a high bandwidth access and does not have to be accessed through another device.
Many SANs rely on the Fibre Channel (FC) protocol. A single FC link can carry data at rates up to 4 gigabits per second (Gb/s) in both directions simultaneously. The FC protocol defines standard media and signaling conventions for transporting data in a serial fashion. It also provides an error correcting channel code and a frame structure for transporting the data. Further, the FC protocol sets out a buffer-credit-based flow control methodology, and creates some common services (e.g. fabric controller, name server). The FC protocol can be applied to various network topologies including point-to-point, ring, and switched fabric. Further details regarding the FC protocol can be found online at www.fibrechannel.org.
FC SANs can be implemented with a number of topologies. The most popular topology is a switched fabric topology, i.e., a fabric made up of switches that interconnect end-node devices. The FC standard defines a fabric as “the entity which interconnects various [end nodes] attached to it and is capable of routing frames by using only the [destination identifier] information in [the] frame header”. As SANs have grown in size, it has been observed that smaller fabrics are generally more reliable and easier to maintain than larger fabrics. It has also been observed that customers seem to prefer fabrics with a small number of large switches over fabrics with a large number of small switches. Accordingly, a trend is expected in SAN technology towards multiple-fabric solutions in which each fabric includes only a small number of large switches.
The FC protocol lacks support for inter-fabric communication. It would be desirable to augment the FC protocol to provide support for inter-network communication. It would further be desirable to make implementation of high-performance, high port count switches more economical.